Chessmetrics#Perceived disadvantages

Chessmetrics is a weighted average of past performance.[http://chessmetrics.com/cm/CM2/Formulas.asp Chessmetrics formulas page] {{webarchive|url=https://web.archive.org/web/20110809102543/http://chessmetrics.com/cm/CM2/Formulas.asp |date=2011-08-09 }} The score considers a player's win percentage against other players weighted by the ratings of the other players and the time elapsed since the match. A 10% increase in performance is equivalent to an increase of 85 rating points.

The weighting of previous matches digresses linearly from 100% for just-finished matches to zero for matches conducted more than two years ago.

Performance rating adjustment after tournament:

:Performance Rating = Average Opponents' Rating + [(PctScore - 0.50) * 850]

Weighting of past tournaments (age is how many months ago the tournament was played):

:100% * (24 - age)

In 2006 economists Charles C. Moul and John V. C. Nye used Chessmetrics to determine the "expected" results of games, and wrote:

Ratings in chess that make use of rigorous statistics to produce good estimates of relative player strength are now relatively common, but comparing ratings across different time periods is often complicated by idiosyncratic changes (cf. Elo, 1968 for the pioneering discussion). Sonas uses the same rating formula throughout our sample and updates this rating monthly instead of annually, as is more common. Moreover, retrospective grading allows him to establish rankings that are unbiased estimates of the "true" relative strengths of players.{{cite SSRN | ssrn=905612 | title=Did the Soviets Collude? A Statistical Analysis of Championship Chess 1940–64 | date=May 2006 | author=Charles C. Moul and John V. C. Nye}}

The system has also been described as "the most complete and resounding attempt made to determine the best chess player in history". However, the system is more accurate in measuring a player's success in competition than quality of play.[http://www.chessbase.com/news/2006/world_champions2006.pdf Computer Analysis of World Chess Champions], M.Guid and I.Bratko, ICGA Journal (Vol 29, No. 2, June 2006, pages 65–73).

The original article on Chessmetrics was published in Chessbase in October 2002.{{ cite web | url=http://www.chessbase.com/newsdetail.asp?newsid=562 | title=The Sonas Rating Formula – Better than Elo? | author=Jeff Sonas | date=22 October 2002 | access-date=2008-07-08 }} Since then, Chessmetrics has become reasonably well known and features numerous articles in Chessbase and The Week in Chess.For instance, Chessmetrics articles on Comparison of top chess players throughout history at Chessbase: [http://www.chessbase.com/newsdetail.asp?newsid=2345 Part 1] [http://www.chessbase.com/newsdetail.asp?newsid=2354 Part 2] [http://www.chessbase.com/newsdetail.asp?newsid=2372 Part 3] [http://www.chessbase.com/newsdetail.asp?newsid=2409 Part 4]

Chess author John L. Watson has also referred to Chessmetrics numbers.

• Chess rating systems

• [http://www.chessmetrics.com/ Chessmetrics site]

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Category:Chess rating systems